The present invention relates to a method for heating plastics by means of laser points from a laser beam on a focal plane, preferably for welding plastics using the laser transmission method. The invention also relates to an apparatus for heating plastics by means of laser beams with the aid of a processing head for accommodating devices for shaping the laser beam.
In order to weld plastics by means of laser beams, it is known in the so-called transmission welding method for a first plastic part that is transparent to the laser beam to be heated at the contact surface with a second plastic part that is absorbent for the laser beam, and for these parts to be welded to one another under the action of pressure. In order to achieve the desired speed at which the laser is moved over the plastic components and, nevertheless, to ensure good welding qualities, it is necessary to install in the beam path a preheating process that ensures that the heating is performed in various steps in a way known per se. It is known for this purpose to use a number of laser beams that are guided pointwise one after the other to bring the plastics material up to a preheating temperature in a first step, and up to the welding temperature in a second step.
The welding of tarpaulins made from coated fabrics, films and sealing webs requires a test structure for testing the strength of the weld seam. When the welding is carried out by means of laser beams, it is likewise necessary to produce an appropriate test structure during the welding process. This normally happens through the production of double welding lines.
In order to split light, it is known to undertake beam splitting such that a number of light outputs from a light source are produced in different directions which have the same beam quality. The light intensity at different light outputs is determined by optical properties of the beam splitter. The space requirement and the costs are, however, relatively high, since each optical output requires all the lens components in order to shape the beam appropriately and to collimate it. This method cannot be applied, above all, when an easy spatial splitting of the light is involved.
It is therefore the object of the present invention to propose a possibility of being able to produce a plurality of laser points on a focal plane while observing good handling, flexibility and also, as far as possible, the use of optical fibers.